In recent years, in an aligning apparatus, e.g., a stage device for an exposure apparatus, which is required for high alignment accuracy, a plane motor type aligning apparatus has been attracting attention. As a plane motor type aligning apparatus, for example, an aligning apparatus described in Japanese Patent Laid-Open No. 08-006642 is available. According to Japanese Patent Laid-Open No. 08-006642, the aligning apparatus uses a movable element obtained by winding a coil around an inductor toothed iron core and a stator obtained by forming tooth-like projections on a magnetic base. The movable element is driven by a pulse motor scheme using a so-called Sawyer's principle. The movable element has an air supply hole. Air is supplied between the stator and movable element to levitate the movable element.
As a plane motor type aligning apparatus which utilizes the Lorentz force, for example, an aligning apparatus described in Japanese Patent Laid-Open No. 11-069764 is available. Japanese Patent Laid-Open No. 11-069764 discloses an aligning apparatus in which a wafer table having a magnet plate is sandwiched by a core table and a top yoke. In this structure, a coil provided to the core plate generates a thrust and a levitating force in the wafer table. Most of the weight of the wafer table is levitated and supported by using a magnetic circuit formed of a core portion, the top yoke, and support columns which support the core portion and top yoke.
Regarding Japanese Patent Laid-Open No. 08-006642, if the movable element is levitated by pneumatic pressure, a problem arises for use in a vacuum. If the driving scheme is the pulse motor scheme using Sawyer's principle, vibration from the stator tends to be transmitted easily, and highly accurate position control is difficult to perform. If the movable element includes a coil, the coil needs a cable for power supply. Accordingly, the coil is susceptible to disturbance from the cable. In this respect, as well, high alignment accuracy control is difficult to perform. When high position accuracy is required in the posture and vertical direction as in an exposure apparatus, with this driving scheme, a fine movement stage for Z tilt direction control must be provided, making the structure complicated.
If the lower core portion is made of a magnetic material as in Japanese Patent Laid-Open No. 11-069764, cogging occurs undesirably, and highly accurate alignment control is difficult to perform.
The present invention has been made in view of the above problems, and has as its object to provide an aligning apparatus, which performs highly accurate alignment while suppressing the influence of coil heat generation.